Interestingly, the original document for Irish nationals gives the date as 1949, rather than the date of independence,
As a result of the above, there is generally no special access to British citizenship for Irish citizens. The facility for those born before 1949 to claim British subject status does not confer British citizenship, although it gives an entitlement to registration as such after five years in the UK.
so your date of 2015 for the Scots wouldn't appear to be correct (have no idea why 1949 is given, maybe someone else might know). This would suggest that Scottish people have a considerable grace period yet (several decades in fact) before they need to choose either/or, and it shouldn't affect the majority of Scots currently living. This of course assumes that the Irish model, as you've posted it, would be carried over to Scotland.